This chapter describes different physical and logical network topologies. It discusses simple topologies like bus, ring, and star as well as hybrid combinations. It also covers enterprise-wide topologies and wide area network topologies. The chapter then summarizes logical transmission methods for different network types, including Ethernet, Token Ring, LocalTalk, FDDI, and ATM.
2. Objectives
Describe the basic and hybrid LAN physical
topologies, their uses, advantages, and
disadvantages
Describe a variety of enterprise-wide and
WAN physical topologies, their uses,
advantages, and disadvantages
Compare the different types of switching used
in data transmission
Understand the transmission methods, or
logical topologies, underlying Ethernet, Token
Ring, LocalTalk, and FDDI networks
3. Simple Physical Topologies
Physical topology
Physical layout of a network
A Bus topology consists of a single cable—called
a bus— connecting all nodes on a network without
intervening connectivity devices
Figure 5-1:
Bus topology
network
5. Simple Physical Topologies
Ring topology
Each node is connected to the two nearest nodes so the entire
network forms a circle
One method for passing data on ring networks is token passing
Active topology
Each workstation transmits data
Figure 5-3:
A typical
ring
network
6. Simple Physical Topologies
Star topology
Every node on the network is connected through
a central device
Figure 5-4:
A typical
star
topology
network
7. Hybrid Physical Topologies
Hybrid topology
Complex combination of the simple physical topologies
Star-wired ring
Star-wired topologies use physical layout of a star in
conjunction with token ring-passing data transmission
method
Figure 5-5:
A star-
wired ring
topology
network
8. Hybrid Physical Topologies
Star-wired bus
In a star-wired bus topology, groups of workstations are
star-connected to hubs and then networked via a single bus
Figure 5-6: A star-wired bus network topology
12. Enterprise-Wide Topologies
Serial backbone
Two or more hubs connected to each other by a single cable
Distributed backbone
Hubs connected to a series of central hubs or routers in a
hierarchy
Figure 5-9:
A simple
distributed
backbone
network
15. Enterprise-Wide Topologies
Parallel Backbone
Collapsed backbone arrangement that consists of more than one
connection from central router or switch to each network
segment
Figure 5-
12: A
parallel
backbone
network
16. Enterprise-Wide Topologies
Mesh networks
Routers are interconnected with other routers, with at least two
pathways connecting each router
Figure 5-13:
An example of
a mesh
network
17. Wide Area Network (WAN)
Topologies
Peer-to-peer topology
WAN with single interconnection points for each
location
Dedicated circuits
Continuous physical or logical connections between two
access points that are leased from a communication
provider
Figure 5-14:
A peer-to-peer
WAN
18. Wide Area Network (WAN)
Topologies
Ring WAN topology
Each site is connected to two other sites so that entire
WAN forms a ring pattern
Figure 5-15: A ring-configured WAN
19. Wide Area Network (WAN)
Topologies
Star WAN topology
Single site acts as the central connection point for several
other points
Figure 5-16:
A star-
configured
WAN
20. Wide Area Network (WAN)
Topologies
Mesh WAN topology
Many directly interconnected locations forming a complex mesh
Figure 5-17: Full-mesh and partial-mesh WANs
21. Wide Area Network (WAN)
Topologies
Tiered WAN topology
Sites connected in star or ring formations are interconnected at
different levels, with interconnection points organized into layers
Figure 5-18: A tiered WAN topology
22. Logical Topologies
Refers to the way in which data are
transmitted between nodes
Describes the way:
Data are packaged in frames
Electrical pulses are sent over network’s physical
media
Logical topology may also be called network
transport system
23. Switching
Component of network’s logical topology that
determines how connections are created
between nodes
Circuit switching
Connection is established between two network nodes
before they begin transmitting data
Message switching
Establishes connection between two devices, transfers
information to second device, and then breaks connection
Packet switching
Breaks data into packets before they are transmitted
24. Ethernet
Carrier Sense Multiple Access with Collision
Detection (CSMA/CD)
The access method used in Ethernet
Collision
In Ethernet networks, the interference of one network node’s
data transmission with another network node’s data
transmission
Jamming
Part of CSMA/CD in which, upon detection of collision,
station issues special 32-bit sequence to indicate to all nodes
on Ethernet segment that its previously transmitted frame
has suffered a collision and should be considered faulty
26. Ethernet
On an Ethernet network, an individual
network segment is known as a collision
domain
Portion of network in which collisions will occur if
two nodes transmit data at same time
Data propagation delay
Length of time data take to travel from one point
on the segment to another point
27. Ethernet
Demand priority
Method for data transmission used by 100BaseVG Ethernet
networks
Demand priority requires an intelligent hub
Figure 5-20:
CSMA/CD versus
demand priority
28. Ethernet
Traditional Ethernet LANs, called shared
Ethernet, supply fixed amount of bandwidth
that must be shared by all devices on a segment
Switch
Device that can separate network segments into
smaller segments, with each segment being
independent of the others and supporting its own
traffic
Switched Ethernet
Newer Ethernet model that enables multiple nodes to
simultaneously transmit and receive data over logical
network segments
30. Ethernet
Gigabit Ethernet
1 Gigabit Ethernet
Ethernet standard for networks that achieve 1-
Gbps maximum throughput
10 Gigabit Ethernet
Standard currently being defined by IEEE 802.3ae
committee
Will allow 10-Gbps throughput
Will include full-duplexing and multimode fiber
requirements
31. Ethernet
Padding
Bytes added to data portion of an Ethernet frame to
make sure this field is at least 46 bytes in size
Ethernet frame types:
IEEE 802.3 (“Ethernet 802.2” or “LLC”)
Novell proprietary 802.3 frame (or “Ethernet 802.3”)
Ethernet II frame
IEEE 802.3 SNAP frame
32. IEEE 802.3 (“Ethernet 802.2” or
“LLC”)
Default frame type for versions 4.x and higher of
Novell NetWare network operating system
Sometimes called LLC frame
In Novell’s lexicon, this frame is called Ethernet 802.2
frame
Figure 5-22: An IEEE 802.3 frame
33. IEEE 802.3 (“Ethernet 802.2” or
“LLC”)
Service Access Point (SAP)
Identifies node or internal process that uses LLC
protocol
Frame Check Sequence (FCS)
This field ensures that data are received just as
they were sent
Cyclical Redundancy Check (CRC)
Algorithm used by FCS field in Ethernet frames
34. Novell Proprietary 802.3 (or
“Ethernet 802.3”)
Original NetWare frame type
Also called:
802.3 Raw
Ethernet 802.3 frame
Figure 5-23: A Novell proprietary 802.3 frame
35. Ethernet II
Original Ethernet frame type developed by
DEC, Intel and Xerox, before IEEE began
to standardize Ethernet
Figure 5-24: An Ethernet II frame
36. IEEE 802.3 SNAP
Adaptation of IEEE 802.3 and Ethernet II
SNAP stands for Sub-Network Access Protocol
Figure 5-25: An IEEE 802.3 SNAP frame
37. Understanding Frame Types
Learning about networks is analogous to
learning a foreign language, with the frame type
being the language’s syntax
Just as you may know the Japanese word for go but
how to use it in a sentence, you may know all about
the IPX/SPX protocol but not how devices handle it
Autosense
Feature of modern NICs that enables a NIC to
automatically sense what types of frames are running
on a network and set itself to that specification
38. Design Considerations for Ethernet
Networks
Cabling
Connectivity devices
Number of stations
Speed
Scalability
Topology
39. LocalTalk
Logical topology designed by Apple
Computer, Inc.
Uses a transmission method called Carrier
Sense Multiple Access/Collision
Avoidance (CSMA/CA)
A teleconnector is a transceiver used on a
LocalTalk network
Macintosh version of TCP/IP is called
MacTCP
40. Token Ring
Token Ring networks use the token passing
routine and a star-ring hybrid physical
topology
The 100-Mbps Token Ring standard is known
as High-Speed Token Ring (HSTR)
On a Token Ring network, one workstation,
called the active monitor, acts as the
controller for token passing
42. Token Ring
Control Access Unit (CAU)
Connectivity device used on a Token Ring
network
Lobe Attachment Module (LAM)
Device that attaches to a CAU to expand the
capacity of that device
43. Token Ring
Token Ring networks with STP cabling may use a
type 1 IBM connector
A DB-9 connector is another type of connector
found on STP Token Ring networks
Figure 5-27: Type 1 IBM and DB-9 Token Ring connectors
44. Token Ring
Media filter
Device that enables two types of cables or connectors to be
linked
Token Ring media filter
Enables DB-9 cable and type 1 IBM cable to be connected
Figure 5-28: A Token Ring media filter
45. Token Ring
Token Ring switching
Like Ethernet networks, Token Ring networks can take
advantage of switching to better utilize limited bandwidth
Token Ring frames
IEEE 802.5 Token Ring frame
IBM Token Ring frame
Figure 5-29: An IBM Token Ring frame
46. Design Considerations for Token
Ring Networks
Cabling
Connectivity devices
Number of stations
Speed
Scalability
Topology
47. Fiber Distributed Data Interface
(FDDI)
Logical topology whose standard was originally specified
by ANSI in mid-1980s and later refined by ISO
Figure 5-30:
A FDDI
network
48. Asynchronous Transfer Mode
(ATM)
Logical topology that relies on a fixed packet
size to achieve data transfer rates up to 9953
Mbps
The fixed packet in ATM is called a cell
A unique aspect of ATM technology is that it
relies on virtual circuits
49. Asynchronous Transfer Mode
(ATM)
ATM uses circuit switching, which allows
ATM to guarantee a specific quality of
service (QOS)
ATM technology can be integrated with
Ethernet or Token Ring networks through the
use of LAN Emulation (LANE)
50. Chapter Summary
A physical topology is the basic layout of a network
Physical topologies are categorized into three
fundamental geometric shapes: bus, ring, and star
Few LANs use the simple physical topologies in
their pure form
Hubs that service star-wired bus or star-wired ring
topologies can be daisy-chained to form a more
complex hybrid topology
Hierarchical hybrid topology can designate hubs at
different layers to perform different functions
51. Chapter Summary
Cabling that connects each hub is called the
backbone
In mesh networks, routers are interconnected with
other routers so at least two pathways connect each
node
WAN topologies use LAN and enterprise-wide
topologies as building blocks, but add more
complexity
Network logical topologies encompass a set of rules
specifying which data are packaged and transmitted
over network media
52. Chapter Summary
Switching is a component of a network’s logical
topology that manages the filtering and
forwarding of packets between nodes on a
network
Ethernet is a networking technology and is by far
the most popular logical topology for LANs today
Ethernet follows a network access method called
CSMA/CD
On heavily trafficked Ethernet networks,
collisions are not uncommon
A switch is a device that can separate a network
into smaller segments, each independent of each
other and supporting its own traffic
53. Chapter Summary
Token Ring networks currently run at either 4 or 16
Mbps, as specified by IEEE 802.5
Token Ring networks use the token-passing routine
and a star-ring hybrid physical topology
FDDI is a networking standard originally specified by
ANSI in mid-1980s and later refined by ISO
ATM relies on a fixed packet size to achieve data
transfer rates up to 9953 Mbps
ATM relies on virtual circuits to determine the
optimal path between sender and receiver